When fabricating semiconductor chips on a wafer are completed, the chips are tested during or after fabrication process or before packaging process for evaluating their designed electrical characteristics partially or entirely.
A probe station is one of the most popular tools for making measurements on the integrated circuits. The probe station is provided with a probe card holder for holding a probe card which applies electric signal to pads of the chips formed on the wafer.
Typically, the probe card is composed of a printed substrate and a plurality of probes mounted on the printed substrate. The printed substrate has a circuitry for electrically connecting probing devices and the probes. The probes are contacted the pads of the chips to be tested.
The wafer placed on a chuck is moved along the x-axis and y-axis to be aligned on the probe card such that the probes are positioned on the respective pads of the chips. And then, the chuck moves in z-axis such that the tips of the probes contact the pads of the chips.
The chips are tested by transmitting electrical signals generated by probe station to the chips via wires patterned on the printed substrate and probe tips.
With the advance of the semiconductor fabrication technologies, a wafer increases in size and, in turn, the number of chips per wafer increases for the purpose of reduction of manufacturing cost and improvement of productivity. In order to effectively test more highly integrated chips on the large wafer, the probe card also becomes larger in size. Such a probe card having a capability to test multiple chips is called a multi-para probe card.
The multi-para probe card is manufactured by transferring cantilever-type probes fabricated by a Micro Electro-Mechanical System (MEMS) and then removing a sacrificial layer after bonding the probes on a ceramic substrate. Here, the ceramic substrate acts as a space transformer for changing the probes from fine pitch to coarse pitch. The ceramic substrate is used since its thermal expansion coefficient and thermal contraction coefficient are similar to those of the silicon wafer. By using the ceramic substrate, it is possible to minimize mismatch between probe tips and chip pads caused by the thermal expansion or contraction of the substrate.
However, the conventional probe card has a drawback in that the probe terminals and the pads of the chips to be tested are mismatched when the temperature changes excessively since the thermal expansion coefficients of the silicon and ceramic are 2.6 ppm/and 6.0 ppm/, respectably. For example, when the temperature increases about 150 degree, the position displacement around the edge of the 12 wafer are 59 μm and 153 μm for the ceramic and the silicon. Accordingly, in a case that the chip pad size is smaller than 180 μm, the probe tip fails to contact the pad.
Also, the conventional probe card fabricated by bonding the cantilever-type probes on the ceramic substrate is disadvantageous in fabrication complexity. Particularly when the probe card is needed to be repaired, it is difficult or impossible to repair the probes individually.